Composite materials such as thermoset resin materials are well known and widely used in the aerospace industry and other industries where materials having a high strength to weight ratio, high temperature tolerance and good corrosion resistance are desirable. Composite structures are often formed by overlapping layers of a fibrous strands or tows impregnated with a thermosetting resin (e.g., graphite fiber impregnated with a matrix material such as epoxy). Fiber placement machines such as the one shown in U.S. Pat. No. 5,110,395, for example, are used to apply a number of individual fiber tows side-by-side to form parts having relatively complex shapes, such as parts having contoured or arcuate surfaces. The fiber placement machine includes a creel assembly comprising a number of spools of tows from which tows are individually fed to a fiber placement head. The tows are fed side-by-side from the head onto the surface of a mandrel or tool, for example, to form a fiber band which is pressed onto the surface by a compaction roller or shoe.
Prior art fiber placement machines such as described above, are operable to lay the fiber tows as the head traverses the surface in only one direction (i.e., forward but not rearward). The fiber placement head is positioned along one edge of the surface and lays a row of tows in one direction along the surface, following which the tows are cut. The head is then moved in a reverse direction and repositioned to a location on the edge of the surface adjacent the first row of tows to lay a second row of tows in the same forward direction. Since the machine does not lay tows while travelling in the reverse direction, the time required for the fiber placement head to travel back along the surface to reposition the head is wasted. For large parts this dead time significantly reduces the efficiency of the fiber placement head.